Techniques for clock recovery following a power outage

ABSTRACT

Clock reference data may be recovered or updated in networks that include line-powered devices and other devices susceptible to power outages. For example, for a mobile information collection network, one or more devices with extended clock holdover may be strategically deployed throughout the mobile information collection network to provide reference clock data. As another example, battery-powered devices may be woken up in order to provide clock reference data to other devices. Alternatively or additionally, the battery-powered devices may be configured to periodically broadcast their clock reference data to other devices.

TECHNICAL BACKGROUND

The reading of electrical energy, water flow, and gas usage has historically been accomplished with human meter readers who came on-site and manually documented meter readings. Over time, this manual meter reading methodology has been enhanced with walk by or drive by reading systems that use radio communications to and from a mobile collector device in a vehicle. Recently, there has been a concerted effort to accomplish meter reading using fixed communication networks that allow data to flow from the meter to a host computer system without human intervention.

Automated systems, such as Automatic Meter Reading (AMR) and Advanced Metering Infrastructure (AMI) systems, may use radio frequency (RF) signals to collect data from transponders attached to meters that measure usage of resources, such as gas, water and electricity. AMR systems use a mobile data collector, such as a handheld computer equipped with RF technology or a vehicle-based RF system, to collect meter data. In this document, terms such as “mobile interrogator”, “interrogator” and “mobile device” will be used to refer to a mobile data collection platform. Such systems may employ a number of different infrastructures for collecting this meter data from the meters. For example, some automated systems obtain data from the meters using a fixed wireless network that includes, for example, a central node, e.g., a collection device, in communication with a number of endpoint nodes (e.g., meter reading devices (MRDs) connected to meters). At the endpoint nodes, the wireless communications circuitry may be incorporated into the meters themselves, such that each endpoint node in the wireless network comprises a meter connected to an MRD that has wireless communication circuitry that enables the MRD to transmit the meter data of the meter to which it is connected. The wireless communication circuitry may include a transponder that may or may not be uniquely identified by a transponder serial number. The endpoint nodes may either transmit their meter data directly to the central node, or indirectly though one or more intermediate bi-directional nodes that serve as repeaters for the meter data of the transmitting node.

Some networks may employ a mesh networking architecture. In such networks, known as “mesh networks,” endpoint nodes are connected to one another through wireless communication links such that each endpoint node has a wireless communication path to a central node. This central node may be commonly referred to by several names including: gatekeeper; collector; and network access point. In this document, terms such as “gatekeeper” and “collector” will most often be used to refer to this functionality. One characteristic of mesh networks is that the component nodes can all connect to one another via one or more “hops.” Due to this characteristic, mesh networks can continue to operate even if a node or a connection breaks down. Accordingly, mesh networks are self-configuring and self-healing, significantly reducing installation and maintenance efforts.

Data collection systems such as electric, gas, and water utility systems tend to fall into two classifications: fixed or mobile network. Each has advantages and disadvantages. A fixed network typically has a tree structure with endpoints at the extreme ends of the tree. These endpoints relay their data toward a central head end by passing data first through a local area network (LAN) including other endpoints, repeaters, and collectors, and then through a wide area network (WAN) to the head end. Data gathered by the head end may be analyzed, stored, presented and/or forwarded to other utility and consumer systems. Some units, such as electricity meters, in a fixed network are always on. Other units, such as gas meters, water meters, and in-home modules, are battery operated and may periodically receive a wake-up signal to tie into the network. This periodic wake-up process can be unilateral at the discretion of the endpoint or the result of a wake-up process initiated by adjacent always-on devices.

A mobile network can be drive-by, fly-by, or walk-by in nature and typically involves a mobile interrogator traveling a predetermined route to gather data from endpoint devices in residential and commercial locations. The mobile interrogator may also issue commands to the endpoint devices. The endpoint devices may include water, gas, and electricity metering and control devices, such as thermostats and load control devices. There is typically little or no communication between endpoint devices themselves, and each endpoint device typically maintains its own history of data for the past collection period. The mobile interrogator wakes up the endpoint devices for the communication exchange. Alternatively, the devices may unilaterally transmit their data periodically so that the mobile interrogator can receive the data whenever it travels by. The collected data is passed from the mobile interrogator to a route manager, and then up to a head end that interfaces to a utility billing system.

When power outages occur in an electric system, connected meters with automated meter reading (AMR) functions may lose their reference clock. Even when local battery power is available, long duration outages can extend beyond the capability of the local battery power source to maintain clock operations. Because modern meter automation systems use a variety of calendar and schedule-based events, this loss of reference time can be critical.

SUMMARY OF THE DISCLOSURE

Clock reference data may be recovered or updated in networks that include line-powered devices and other devices susceptible to power outages. For example, for a mobile information collection network, one or more devices with extended clock holdover may be strategically deployed throughout the mobile information collection network to provide reference clock data. As another example, battery-powered devices may be woken up in order to provide clock reference data to other devices. Alternatively or additionally, the battery-powered devices may be configured to periodically broadcast their clock reference data to other devices.

One exemplary embodiment is directed to a system for efficiently updating clock reference data after a power outage in a mobile information collection network. The system may include one or more mobile mode communication nodes configured to communicate information to a mobile device when the mobile device moves within a physical proximity of the mobile mode communication nodes. The system may further include an extended clock holdover node configured to maintain the clock reference data after the power outage for a longer duration than the mobile mode communication nodes. After power is restored at the mobile mode communication nodes, the extended clock holdover node may be configured to provide the clock reference data to the mobile mode communication nodes.

Another exemplary embodiment is directed to a method for obtaining clock reference data from a battery powered device in a system comprising a plurality of mobile mode communication nodes configured to communicate data to a mobile device when the mobile device moves within a physical proximity of each of the mobile mode communication nodes. At least one of the mobile mode communication nodes includes a battery-powered device. The method involves sending a wake-up signal and a clock reference request signal to the battery-powered device and receiving the requested clock reference data from the battery-powered device.

Yet another exemplary embodiment is directed to a system for obtaining clock reference data by a line-powered communication node for use in a fixed wireless network comprising a plurality of communication nodes in wireless communication with a control node. Each communication node has a wireless communication path to the control node that is either a direct path or an indirect path through one or more other communication nodes that serve as repeaters. The system includes a line-powered communication node and a battery-powered communication node that periodically transmits clock reference data as part of a fixed network message. The line-powered communication node is configured to receive the clock reference data transmitted by the battery-powered communication node.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description of various embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings exemplary embodiments of various aspects of the invention; however, the invention is not limited to the specific methods and instrumentalities disclosed. In the drawings:

FIG. 1 is a diagram of an exemplary metering system;

FIG. 2 expands upon the diagram of FIG. 1 and illustrates an exemplary metering system in greater detail;

FIG. 3A is a block diagram illustrating an exemplary collector;

FIG. 3B is a block diagram illustrating an exemplary meter;

FIG. 4 is a diagram of an example subnet of a wireless network for collecting data from remote devices;

FIG. 5A is a diagram of an exemplary prior art mobile information collection network;

FIG. 5B is a diagram of an exemplary mobile information collection network with an extended clock holdover device;

FIG. 6 is a process flow diagram illustrating an example method for obtaining clock reference data from a battery-powered device; and

FIG. 7 is a process flow diagram illustrating an example method for updating clock reference data.

DETAILED DESCRIPTION

Exemplary systems and methods for gathering meter data are described below with reference to FIGS. 1-7. It will be appreciated by those of ordinary skill in the art that the description given herein with respect to those figures is for exemplary purposes only and is not intended in any way to limit the scope of potential embodiments.

Generally, a plurality of meter devices, which operate to track usage of a service or commodity such as, for example, electricity, water, and gas, are operable to wirelessly communicate. One or more devices, referred to herein as “collectors,” are provided that “collect” data transmitted by the other meter devices so that it can be accessed by other computer systems. The collectors receive and compile metering data from a plurality of meter devices via wireless communications. A data collection server may communicate with the collectors to retrieve the compiled meter data.

FIG. 1 provides a diagram of one exemplary metering system 110. System 110 comprises a plurality of meters 114, which are operable to sense and record consumption or usage of a service or commodity such as, for example, electricity, water, or gas. Meters 114 may be located at customer premises such as, for example, a home or place of business. Meters 114 comprise circuitry for measuring the consumption of the service or commodity being consumed at their respective locations and for generating data reflecting the consumption, as well as other data related thereto. Meters 114 may also comprise circuitry for wirelessly transmitting data generated by the meter to a remote location. Meters 114 may further comprise circuitry for receiving data, commands or instructions wirelessly as well. Meters that are operable to both receive and transmit data may be referred to as “bi-directional” or “two-way” meters, while meters that are only capable of transmitting data may be referred to as “transmit-only” or “one-way” meters. In bi-directional meters, the circuitry for transmitting and receiving may comprise a transceiver. In an illustrative embodiment, meters 114 may be, for example, electricity meters manufactured by Elster Solutions, LLC and marketed under the tradename REX.

System 110 further comprises collectors 116. In one embodiment, collectors 116 are also meters operable to detect and record usage of a service or commodity such as, for example, electricity, water, or gas. In addition, collectors 116 are operable to send data to and receive data from meters 114. Thus, like the meters 114, the collectors 116 may comprise both circuitry for measuring the consumption of a service or commodity and for generating data reflecting the consumption and circuitry for transmitting and receiving data. In one embodiment, collector 116 and meters 114 communicate with and amongst one another using any one of several wireless techniques such as, for example, frequency hopping spread spectrum (FHSS) and direct sequence spread spectrum (DSSS).

A collector 116 and the meters 114 with which it communicates define a subnet/LAN 120 of system 110. As used herein, meters 114 and collectors 116 may be referred to as “nodes” in the subnet 120. In each subnet/LAN 120, each meter transmits data related to consumption of the commodity being metered at the meter's location. The collector 116 receives the data transmitted by each meter 114, effectively “collecting” it, and then periodically transmits the data from all of the meters in the subnet/LAN 120 to a data collection server 206. The data collection server 206 stores the data for analysis and preparation of bills, for example. The data collection server 206 may be a specially programmed general purpose computing system and may communicate with collectors 116 via a network 112. The network 112 may comprise any form of network, including a wireless network or a fixed-wire network, such as a local area network (LAN), a wide area network, the Internet, an intranet, a telephone network, such as the public switched telephone network (PSTN), a Frequency Hopping Spread Spectrum (FHSS) radio network, a mesh network, a Wi-Fi (802.11) network, a Wi-Max (802.16) network, a land line (POTS) network, or any combination of the above.

Referring now to FIG. 2, further details of the metering system 110 are shown. Typically, the system will be operated by a utility company or a company providing information technology services to a utility company. As shown, the system 110 comprises a network management server 202, a network management system (NMS) 204 and the data collection server 206 that together manage one or more subnets/LANs 120 and their constituent nodes. The NMS 204 tracks changes in network state, such as new nodes registering/unregistering with the system 110, node communication paths changing, etc. This information is collected for each subnet/LAN 120 and is detected and forwarded to the network management server 202 and data collection server 206.

Each of the meters 114 and collectors 116 is assigned an identifier (LAN ID) that uniquely identifies that meter or collector on its subnet/LAN 120. In this embodiment, communication between nodes (i.e., the collectors and meters) and the system 110 is accomplished using the LAN ID. However, it is preferable for operators of a utility to query and communicate with the nodes using their own identifiers. To this end, a marriage file 208 may be used to correlate a utility's identifier for a node (e.g., a utility serial number) with both a manufacturer serial number (i.e., a serial number assigned by the manufacturer of the meter) and the LAN ID for each node in the subnet/LAN 120. In this manner, the utility can refer to the meters and collectors by the utilities identifier, while the system can employ the LAN ID for the purpose of designating particular meters during system communications.

A device configuration database 210 stores configuration information regarding the nodes. For example, in the metering system 200, the device configuration database may include data regarding time of use (TOU) switchpoints, etc. for the meters 114 and collectors 116 communicating in the system 110. A data collection requirements database 212 contains information regarding the data to be collected on a per node basis. For example, a utility may specify that metering data such as load profile, demand, TOU, etc. is to be collected from particular meter(s) 114 a. Reports 214 containing information on the network configuration may be automatically generated or in accordance with a utility request.

The network management system (NMS) 204 maintains a database describing the current state of the global fixed network system (current network state 220) and a database describing the historical state of the system (historical network state 222). The current network state 220 contains data regarding current meter-to-collector assignments, etc. for each subnet/LAN 120. The historical network state 222 is a database from which the state of the network at a particular point in the past can be reconstructed. The NMS 204 is responsible for, amongst other things, providing reports 214 about the state of the network. The NMS 204 may be accessed via an API 220 that is exposed to a user interface 216 and a Customer Information System (CIS) 218. Other external interfaces may also be implemented. In addition, the data collection requirements stored in the database 212 may be set via the user interface 216 or CIS 218.

The data collection server 206 collects data from the nodes (e.g., collectors 116) and stores the data in a database 224. The data includes metering information, such as energy consumption and may be used for billing purposes, etc. by a utility provider.

The network management server 202, network management system 204 and data collection server 206 communicate with the nodes in each subnet/LAN 120 via network 110.

FIG. 3A is a block diagram illustrating further details of one embodiment of a collector 116. Although certain components are designated and discussed with reference to FIG. 3A, it should be appreciated that the invention is not limited to such components. In fact, various other components typically found in an electronic meter may be a part of collector 116, but have not been shown in FIG. 3A for the purposes of clarity and brevity. Also, the invention may use other components to accomplish the operation of collector 116. The components that are shown and the functionality described for collector 116 are provided as examples, and are not meant to be exclusive of other components or other functionality.

As shown in FIG. 3A, collector 116 may comprise metering circuitry 304 that performs measurement of consumption of a service or commodity and a processor 305 that controls the overall operation of the metering functions of the collector 116. The collector 116 may further comprise a display 310 for displaying information such as measured quantities and meter status and a memory 312 for storing data. The collector 116 further comprises wireless LAN communications circuitry 306 for communicating wirelessly with the meters 114 in a subnet/LAN and a network interface 308 for communication over the network 112.

In one embodiment, the metering circuitry 304, processor 305, display 310 and memory 312 are implemented using an A3 ALPHA meter available from Elster Solutions, LLC. In that embodiment, the wireless LAN communications circuitry 306 may be implemented by a LAN Option Board (e.g., a 900 MHz two-way radio) installed within the A3 ALPHA meter, and the network interface 308 may be implemented by a WAN Option Board (e.g., a telephone modem) also installed within the A3 ALPHA meter. In this embodiment, the WAN Option Board 308 routes messages from network 112 (via interface port 302) to either the meter processor 305 or the LAN Option Board 306. LAN Option Board 306 may use a transceiver (not shown), for example a 900 MHz radio, to communicate data to meters 114. Also, LAN Option Board 306 may have sufficient memory to store data received from meters 114. This data may include, but is not limited to the following: current billing data (e.g., the present values stored and displayed by meters 114), previous billing period data, previous season data, and load profile data.

LAN Option Board 306 may be capable of synchronizing its time to a real time clock (not shown) in A3 ALPHA meter, thereby synchronizing the LAN reference time to the time in the meter. The processing necessary to carry out the communication functionality and the collection and storage of metering data of the collector 116 may be handled by the processor 305 and/or additional processors (not shown) in the LAN Option Board 306 and the WAN Option Board 308.

The responsibility of a collector 116 is wide and varied. Generally, collector 116 is responsible for managing, processing and routing data communicated between the collector and network 112 and between the collector and meters 114. Collector 116 may continually or intermittently read the current data from meters 114 and store the data in a database (not shown) in collector 116. Such current data may include but is not limited to the total kWh usage, the Time-Of-Use (TOU) kWh usage, peak kW demand, and other energy consumption measurements and status information. Collector 116 also may read and store previous billing and previous season data from meters 114 and store the data in the database in collector 116. The database may be implemented as one or more tables of data within the collector 116.

FIG. 3B is a block diagram of an exemplary embodiment of a meter 114 that may operate in the system 110 of FIGS. 1 and 2. As shown, the meter 114 comprises metering circuitry 304′ for measuring the amount of a service or commodity that is consumed, a processor 305′ that controls the overall functions of the meter, a display 310′ for displaying meter data and status information, and a memory 312′ for storing data and program instructions. The meter 114 further comprises wireless communications circuitry 306′ for transmitting and receiving data to/from other meters 114 or a collector 116.

Referring again to FIG. 1, in the exemplary embodiment shown, a collector 116 directly communicates with only a subset of the plurality of meters 114 in its particular subnet/LAN. Meters 114 with which collector 116 directly communicates may be referred to as “level one” meters 114 a. The level one meters 114 a are said to be one “hop” from the collector 116. Communications between collector 116 and meters 114 other than level one meters 114 a are relayed through the level one meters 114 a. Thus, the level one meters 114 a operate as repeaters for communications between collector 116 and meters 114 located further away in subnet 120.

Each level one meter 114 a typically will only be in range to directly communicate with only a subset of the remaining meters 114 in the subnet 120. The meters 114 with which the level one meters 114 a directly communicate may be referred to as level two meters 114 b. Level two meters 114 b are one “hop” from level one meters 114 a, and therefore two “hops” from collector 116. Level two meters 114 b operate as repeaters for communications between the level one meters 114 a and meters 114 located further away from collector 116 in the subnet 120.

While only three levels of meters are shown (collector 116, first level 114 a, second level 114 b) in FIG. 1, a subnet 120 may comprise any number of levels of meters 114. For example, a subnet 120 may comprise one level of meters but might also comprise sixteen or more levels of meters 114. In an embodiment wherein a subnet comprises sixteen levels of meters 114, as many as 2048 meters might be registered with a single collector 116.

As mentioned above, each meter 114 and collector 116 that is installed in the system 110 has a unique identifier (LAN ID) stored thereon that uniquely identifies the device from all other devices in the system 110. Additionally, meters 114 operating in a subnet 120 comprise information including the following: data identifying the collector with which the meter is registered; the level in the subnet at which the meter is located; the repeater meter at the prior level with which the meter communicates to send and receive data to/from the collector; an identifier indicating whether the meter is a repeater for other nodes in the subnet; and if the meter operates as a repeater, the identifier that uniquely identifies the repeater within the particular subnet, and the number of meters for which it is a repeater. Collectors 116 have stored thereon all of this same data for all meters 114 that are registered therewith. Thus, collector 116 comprises data identifying all nodes registered therewith as well as data identifying the registered path by which data is communicated from the collector to each node. Each meter 114 therefore has a designated communications path to the collector that is either a direct path (e.g., all level one nodes) or an indirect path through one or more intermediate nodes that serve as repeaters.

Information is transmitted in this embodiment in the form of packets. For most network tasks such as, for example, reading meter data, collector 116 communicates with meters 114 in the subnet 120 using point-to-point transmissions. For example, a message or instruction from collector 116 is routed through the designated set of repeaters to the desired meter 114. Similarly, a meter 114 communicates with collector 116 through the same set of repeaters, but in reverse.

In some instances, however, collector 116 may need to quickly communicate information to all meters 114 located in its subnet 120. Accordingly, collector 116 may issue a broadcast message that is meant to reach all nodes in the subnet 120. The broadcast message may be referred to as a “flood broadcast message.” A flood broadcast originates at collector 116 and propagates through the entire subnet 120 one level at a time. For example, collector 116 may transmit a flood broadcast to all first level meters 114 a. The first level meters 114 a that receive the message pick a random time slot and retransmit the broadcast message to second level meters 114 b. Any second level meter 114 b can accept the broadcast, thereby providing better coverage from the collector out to the end point meters. Similarly, the second level meters 114 b that receive the broadcast message pick a random time slot and communicate the broadcast message to third level meters. This process continues out until the end nodes of the subnet. Thus, a broadcast message gradually propagates outward from the collector to the nodes of the subnet 120.

The flood broadcast packet header contains information to prevent nodes from repeating the flood broadcast packet more than once per level. For example, within a flood broadcast message, a field might exist that indicates to meters/nodes which receive the message, the level of the subnet the message is located; only nodes at that particular level may re-broadcast the message to the next level. If the collector broadcasts a flood message with a level of 1, only level 1 nodes may respond. Prior to re-broadcasting the flood message, the level 1 nodes increment the field to 2 so that only level 2 nodes respond to the broadcast. Information within the flood broadcast packet header ensures that a flood broadcast will eventually die out.

Generally, a collector 116 issues a flood broadcast several times, e.g. five times, successively to increase the probability that all meters in the subnet 120 receive the broadcast. A delay is introduced before each new broadcast to allow the previous broadcast packet time to propagate through all levels of the subnet.

Meters 114 may have a clock formed therein. However, meters 114 often undergo power interruptions that can interfere with the operation of any clock therein. Accordingly, the clocks internal to meters 114 cannot be relied upon to provide an accurate time reading. Having the correct time is necessary, however, when time of use metering is being employed. Indeed, in an embodiment, time of use schedule data may also be comprised in the same broadcast message as the time. Accordingly, collector 116 periodically flood broadcasts the real time to meters 114 in subnet 120. Meters 114 use the time broadcasts to stay synchronized with the rest of the subnet 120. In an illustrative embodiment, collector 116 broadcasts the time every 15 minutes. The broadcasts may be made near the middle of 15 minute clock boundaries that are used in performing load profiling and time of use (TOU) schedules so as to minimize time changes near these boundaries. Maintaining time synchronization is important to the proper operation of the subnet 120. Accordingly, lower priority tasks performed by collector 116 may be delayed while the time broadcasts are performed.

In an illustrative embodiment, the flood broadcasts transmitting time data may be repeated, for example, five times, so as to increase the probability that all nodes receive the time. Furthermore, where time of use schedule data is communicated in the same transmission as the timing data, the subsequent time transmissions allow a different piece of the time of use schedule to be transmitted to the nodes.

Exception messages are used in subnet 120 to transmit unexpected events that occur at meters 114 to collector 116. In an embodiment, the first 4 seconds of every 32-second period are allocated as an exception window for meters 114 to transmit exception messages. Meters 114 transmit their exception messages early enough in the exception window so the message has time to propagate to collector 116 before the end of the exception window. Collector 116 may process the exceptions after the 4-second exception window. Generally, a collector 116 acknowledges exception messages, and collector 116 waits until the end of the exception window to send this acknowledgement.

In an illustrative embodiment, exception messages are configured as one of three different types of exception messages: local exceptions, which are handled directly by the collector 116 without intervention from data collection server 206; an immediate exception, which is generally relayed to data collection server 206 under an expedited schedule; and a daily exception, which is communicated to the communication server 122 on a regular schedule.

Exceptions are processed as follows. When an exception is received at collector 116, the collector 116 identifies the type of exception that has been received. If a local exception has been received, collector 116 takes an action to remedy the problem. For example, when collector 116 receives an exception requesting a “node scan request” such as discussed below, collector 116 transmits a command to initiate a scan procedure to the meter 114 from which the exception was received.

If an immediate exception type has been received, collector 116 makes a record of the exception. An immediate exception might identify, for example, that there has been a power outage. Collector 116 may log the receipt of the exception in one or more tables or files. In an illustrative example, a record of receipt of an immediate exception is made in a table referred to as the “Immediate Exception Log Table.” Collector 116 then waits a set period of time before taking further action with respect to the immediate exception. For example, collector 116 may wait 64 seconds. This delay period allows the exception to be corrected before communicating the exception to the data collection server 206. For example, where a power outage was the cause of the immediate exception, collector 116 may wait a set period of time to allow for receipt of a message indicating the power outage has been corrected.

If the exception has not been corrected, collector 116 communicates the immediate exception to data collection server 206. For example, collector 116 may initiate a dial-up connection with data collection server 206 and download the exception data. After reporting an immediate exception to data collection server 206, collector 116 may delay reporting any additional immediate exceptions for a period of time such as ten minutes. This is to avoid reporting exceptions from other meters 114 that relate to, or have the same cause as, the exception that was just reported.

If a daily exception was received, the exception is recorded in a file or a database table. Generally, daily exceptions are occurrences in the subnet 120 that need to be reported to data collection server 206, but are not so urgent that they need to be communicated immediately. For example, when collector 116 registers a new meter 114 in subnet 120, collector 116 records a daily exception identifying that the registration has taken place. In an illustrative embodiment, the exception is recorded in a database table referred to as the “Daily Exception Log Table.” Collector 116 communicates the daily exceptions to data collection server 206. Generally, collector 116 communicates the daily exceptions once every 24 hours.

In the present embodiment, a collector assigns designated communications paths to meters with bi-directional communication capability, and may change the communication paths for previously registered meters if conditions warrant. For example, when a collector 116 is initially brought into system 110, it needs to identify and register meters in its subnet 120. A “node scan” refers to a process of communication between a collector 116 and meters 114 whereby the collector may identify and register new nodes in a subnet 120 and allow previously registered nodes to switch paths. A collector 116 can implement a node scan on the entire subnet, referred to as a “full node scan,” or a node scan can be performed on specially identified nodes, referred to as a “partial node scan.”

A full node scan may be performed, for example, when a collector is first installed. The collector 116 must identify and register nodes from which it will collect usage data. The collector 116 initiates a node scan by broadcasting a request, which may be referred to as a Node Scan Procedure request. Generally, the Node Scan Procedure request directs that all unregistered meters 114 or nodes that receive the request respond to the collector 116. The request may comprise information such as the unique address of the collector that initiated the procedure. The signal by which collector 116 transmits this request may have limited strength and therefore is detected only at meters 114 that are in proximity of collector 116. Meters 114 that receive the Node Scan Procedure request respond by transmitting their unique identifier as well as other data.

For each meter from which the collector receives a response to the Node Scan Procedure request, the collector tries to qualify the communications path to that meter before registering the meter with the collector. That is, before registering a meter, the collector 116 attempts to determine whether data communications with the meter will be sufficiently reliable. In one embodiment, the collector 116 determines whether the communication path to a responding meter is sufficiently reliable by comparing a Received Signal Strength Indication (RSSI) value (i.e., a measurement of the received radio signal strength) measured with respect to the received response from the meter to a selected threshold value. For example, the threshold value may be −80 dBm. RSSI values above this threshold would be deemed sufficiently reliable. In another embodiment, qualification is performed by transmitting a predetermined number of additional packets to the meter, such as ten packets, and counting the number of acknowledgements received back from the meter. If the number of acknowledgments received is greater than or equal to a selected threshold (e.g., 8 out of 10), then the path is considered to be reliable. In other embodiments, a combination of the two qualification techniques may be employed.

If the qualification threshold is not met, the collector 116 may add an entry for the meter to a “Straggler Table.” The entry includes the meter's LAN ID, its qualification score (e.g., 5 out of 10; or its RSSI value), its level (in this case level one) and the unique ID of its parent (in this case the collector's ID).

If the qualification threshold is met or exceeded, the collector 116 registers the node. Registering a meter 114 comprises updating a list of the registered nodes at collector 116. For example, the list may be updated to identify the meter's system-wide unique identifier and the communication path to the node. Collector 116 also records the meter's level in the subnet (i.e. whether the meter is a level one node, level two node, etc.), whether the node operates as a repeater, and if so, the number of meters for which it operates as a repeater. The registration process further comprises transmitting registration information to the meter 114. For example, collector 116 forwards to meter 114 an indication that it is registered, the unique identifier of the collector with which it is registered, the level the meter exists at in the subnet, and the unique identifier of its parent meter that will server as a repeater for messages the meter may send to the collector. In the case of a level one node, the parent is the collector itself. The meter stores this data and begins to operate as part of the subnet by responding to commands from its collector 116.

Qualification and registration continues for each meter that responds to the collector's initial Node Scan Procedure request. The collector 116 may rebroadcast the Node Scan Procedure additional times so as to insure that all meters 114 that may receive the Node Scan Procedure have an opportunity for their response to be received and the meter qualified as a level one node at collector 116.

The node scan process then continues by performing a similar process as that described above at each of the now registered level one nodes. This process results in the identification and registration of level two nodes. After the level two nodes are identified, a similar node scan process is performed at the level two nodes to identify level three nodes, and so on.

Specifically, to identify and register meters that will become level two meters, for each level one meter, in succession, the collector 116 transmits a command to the level one meter, which may be referred to as an “Initiate Node Scan Procedure” command. This command instructs the level one meter to perform its own node scan process. The request comprises several data items that the receiving meter may use in completing the node scan. For example, the request may comprise the number of timeslots available for responding nodes, the unique address of the collector that initiated the request, and a measure of the reliability of the communications between the target node and the collector. As described below, the measure of reliability may be employed during a process for identifying more reliable paths for previously registered nodes.

The meter that receives the Initiate Node Scan Response request responds by performing a node scan process similar to that described above. More specifically, the meter broadcasts a request to which all unregistered nodes may respond. The request comprises the number of timeslots available for responding nodes (which is used to set the period for the node to wait for responses), the unique address of the collector that initiated the node scan procedure, a measure of the reliability of the communications between the sending node and the collector (which may be used in the process of determining whether a meter's path may be switched as described below), the level within the subnet of the node sending the request, and an RSSI threshold (which may also be used in the process of determining whether a registered meter's path may be switched). The meter issuing the node scan request then waits for and receives responses from unregistered nodes. For each response, the meter stores in memory the unique identifier of the responding meter. This information is then transmitted to the collector.

For each unregistered meter that responded to the node scan issued by the level one meter, the collector attempts again to determine the reliability of the communication path to that meter. In one embodiment, the collector sends a “Qualify Nodes Procedure” command to the level one node which instructs the level one node to transmit a predetermined number of additional packets to the potential level two node and to record the number of acknowledgements received back from the potential level two node. This qualification score (e.g., 8 out of 10) is then transmitted back to the collector, which again compares the score to a qualification threshold. In other embodiments, other measures of the communications reliability may be provided, such as an RSSI value.

If the qualification threshold is not met, then the collector adds an entry for the node in the Straggler Table, as discussed above. However, if there already is an entry in the Straggler Table for the node, the collector will update that entry only if the qualification score for this node scan procedure is better than the recorded qualification score from the prior node scan that resulted in an entry for the node.

If the qualification threshold is met or exceeded, the collector 116 registers the node. Again, registering a meter 114 at level two comprises updating a list of the registered nodes at collector 116. For example, the list may be updated to identify the meter's unique identifier and the level of the meter in the subnet. Additionally, the collector's 116 registration information is updated to reflect that the meter 114 from which the scan process was initiated is identified as a repeater (or parent) for the newly registered node. The registration process further comprises transmitting information to the newly registered meter as well as the meter that will serve as a repeater for the newly added node. For example, the node that issued the node scan response request is updated to identify that it operates as a repeater and, if it was previously registered as a repeater, increments a data item identifying the number of nodes for which it serves as a repeater. Thereafter, collector 116 forwards to the newly registered meter an indication that it is registered, an identification of the collector 116 with which it is registered, the level the meter exists at in the subnet, and the unique identifier of the node that will serve as its parent, or repeater, when it communicates with the collector 116.

The collector then performs the same qualification procedure for each other potential level two node that responded to the level one node's node scan request. Once that process is completed for the first level one node, the collector initiates the same procedure at each other level one node until the process of qualifying and registering level two nodes has been completed at each level one node. Once the node scan procedure has been performed by each level one node, resulting in a number of level two nodes being registered with the collector, the collector will then send the Initiate Node Scan Response command to each level two node, in turn. Each level two node will then perform the same node scan procedure as performed by the level one nodes, potentially resulting in the registration of a number of level three nodes. The process is then performed at each successive node, until a maximum number of levels is reached (e.g., seven levels) or no unregistered nodes are left in the subnet.

It will be appreciated that in the present embodiment, during the qualification process for a given node at a given level, the collector qualifies the last “hop” only. For example, if an unregistered node responds to a node scan request from a level four node, and therefore, becomes a potential level five node, the qualification score for that node is based on the reliability of communications between the level four node and the potential level five node (i.e., packets transmitted by the level four node versus acknowledgments received from the potential level five node), not based on any measure of the reliability of the communications over the full path from the collector to the potential level five node. In other embodiments, of course, the qualification score could be based on the full communication path.

At some point, each meter will have an established communication path to the collector which will be either a direct path (i.e., level one nodes) or an indirect path through one or more intermediate nodes that serve as repeaters. If during operation of the network, a meter registered in this manner fails to perform adequately, it may be assigned a different path or possibly to a different collector as described below.

As previously mentioned, a full node scan may be performed when a collector 116 is first introduced to a network. At the conclusion of the full node scan, a collector 116 will have registered a set of meters 114 with which it communicates and reads metering data. Full node scans might be periodically performed by an installed collector to identify new meters 114 that have been brought on-line since the last node scan and to allow registered meters to switch to a different path.

In addition to the full node scan, collector 116 may also perform a process of scanning specific meters 114 in the subnet 120, which is referred to as a “partial node scan.” For example, collector 116 may issue a specific request to a meter 114 to perform a node scan outside of a full node scan when on a previous attempt to scan the node, the collector 116 was unable to confirm that the particular meter 114 received the node scan request. Also, a collector 116 may request a partial node scan of a meter 114 when during the course of a full node scan the collector 116 was unable to read the node scan data from the meter 114. Similarly, a node scan retry will be performed when an exception procedure requesting an immediate node scan is received from a meter 114.

The system 110 also automatically reconfigures to accommodate a new meter 114 that may be added. More particularly, the system identifies that the new meter has begun operating and identifies a path to a collector 116 that will become responsible for collecting the metering data. Specifically, the new meter will broadcast an indication that it is unregistered. In one embodiment, this broadcast might be, for example, embedded in, or relayed as part of a request for an update of the real time as described above. The broadcast will be received at one of the registered meters 114 in proximity to the meter that is attempting to register. The registered meter 114 forwards the time to the meter that is attempting to register. The registered node also transmits an exception request to its collector 116 requesting that the collector 116 implement a node scan, which presumably will locate and register the new meter. The collector 116 then transmits a request that the registered node perform a node scan. The registered node will perform the node scan, during which it requests that all unregistered nodes respond. Presumably, the newly added, unregistered meter will respond to the node scan. When it does, the collector will then attempt to qualify and then register the new node in the same manner as described above.

Once a communication path between the collector and a meter is established, the meter can begin transmitting its meter data to the collector and the collector can transmit data and instructions to the meter. As mentioned above, data is transmitted in packets. “Outbound” packets are packets transmitted from the collector to a meter at a given level. In one embodiment, outbound packets contain the following fields, but other fields may also be included:

Length—the length of the packet; SrcAddr—source address—in this case, the ID of the collector; DestAddr—the LAN ID of the meter to which the packet addressed; RptPath—the communication path to the destination meter (i.e., the list of identifiers of each repeater in the path from the collector to the destination node); and Data—the payload of the packet. The packet may also include integrity check information (e.g., CRC), a pad to fill-out unused portions of the packet and other control information. When the packet is transmitted from the collector, it will only be forwarded on to the destination meter by those repeater meters whose identifiers appear in the RptPath field. Other meters that may receive the packet, but that are not listed in the path identified in the RptPath field will not repeat the packet.

“Inbound” packets are packets transmitted from a meter at a given level to the collector. In one embodiment, inbound packets contain the following fields, but other fields may also be included:

Length—the length of the packet; SrcAddr—source address—the address of the meter that initiated the packet; DestAddr—the ID of the collector to which the packet is to be transmitted; RptAddr—the ID of the parent node that serves as the next repeater for the sending node; Data—the payload of the packet; Because each meter knows the identifier of its parent node (i.e., the node in the next lower level that serves as a repeater for the present node), an inbound packet need only identify who is the next parent. When a node receives an inbound packet, it checks to see if the RptAddr matches its own identifier. If not, it discards the packet. If so, it knows that it is supposed to forward the packet on toward the collector. The node will then replace the RptAddr field with the identifier of its own parent and will then transmit the packet so that its parent will receive it. This process will continue through each repeater at each successive level until the packet reaches the collector.

For example, suppose a meter at level three initiates transmission of a packet destined for its collector. The level three node will insert in the RptAddr field of the inbound packet the identifier of the level two node that serves as a repeater for the level three node. The level three node will then transmit the packet. Several level two nodes may receive the packet, but only the level two node having an identifier that matches the identifier in the RptAddr field of the packet will acknowledge it. The other will discard it. When the level two node with the matching identifier receives the packet, it will replace the RptAddr field of the packet with the identifier of the level one packet that serves as a repeater for that level two packet, and the level two packet will then transmit the packet. This time, the level one node having the identifier that matches the RptAddr field will receive the packet. The level one node will insert the identifier of the collector in the RptAddr field and will transmit the packet. The collector will then receive the packet to complete the transmission.

A collector 116 periodically retrieves meter data from the meters that are registered with it. For example, meter data may be retrieved from a meter every 4 hours. Where there is a problem with reading the meter data on the regularly scheduled interval, the collector will try to read the data again before the next regularly scheduled interval. Nevertheless, there may be instances wherein the collector 116 is unable to read metering data from a particular meter 114 for a prolonged period of time. The meters 114 store an indication of when they are read by their collector 116 and keep track of the time since their data has last been collected by the collector 116. If the length of time since the last reading exceeds a defined threshold, such as for example, 18 hours, presumably a problem has arisen in the communication path between the particular meter 114 and the collector 116. Accordingly, the meter 114 changes its status to that of an unregistered meter and attempts to locate a new path to a collector 116 via the process described above for a new node. Thus, the exemplary system is operable to reconfigure itself to address inadequacies in the system.

In some instances, while a collector 116 may be able to retrieve data from a registered meter 114 occasionally, the level of success in reading the meter may be inadequate. For example, if a collector 116 attempts to read meter data from a meter 114 every 4 hours but is able to read the data, for example, only 70 percent of the time or less, it may be desirable to find a more reliable path for reading the data from that particular meter. Where the frequency of reading data from a meter 114 falls below a desired success level, the collector 116 transmits a message to the meter 114 to respond to node scans going forward. The meter 114 remains registered but will respond to node scans in the same manner as an unregistered node as described above. In other embodiments, all registered meters may be permitted to respond to node scans, but a meter will only respond to a node scan if the path to the collector through the meter that issued the node scan is shorter (i.e., less hops) than the meter's current path to the collector. A lesser number of hops is assumed to provide a more reliable communication path than a longer path. A node scan request always identifies the level of the node that transmits the request, and using that information, an already registered node that is permitted to respond to node scans can determine if a potential new path to the collector through the node that issued the node scan is shorter than the node's current path to the collector.

If an already registered meter 114 responds to a node scan procedure, the collector 116 recognizes the response as originating from a registered meter but that by re-registering the meter with the node that issued the node scan, the collector may be able to switch the meter to a new, more reliable path. The collector 116 may verify that the RSSI value of the node scan response exceeds an established threshold. If it does not, the potential new path will be rejected. However, if the RSSI threshold is met, the collector 116 will request that the node that issued the node scan perform the qualification process described above (i.e., send a predetermined number of packets to the node and count the number of acknowledgements received). If the resulting qualification score satisfies a threshold, then the collector will register the node with the new path. The registration process comprises updating the collector 116 and meter 114 with data identifying the new repeater (i.e. the node that issued the node scan) with which the updated node will now communicate. Additionally, if the repeater has not previously performed the operation of a repeater, the repeater would need to be updated to identify that it is a repeater. Likewise, the repeater with which the meter previously communicated is updated to identify that it is no longer a repeater for the particular meter 114. In other embodiments, the threshold determination with respect to the RSSI value may be omitted. In such embodiments, only the qualification of the last “hop” (i.e., sending a predetermined number of packets to the node and counting the number of acknowledgements received) will be performed to determine whether to accept or reject the new path.

In some instances, a more reliable communication path for a meter may exist through a collector other than that with which the meter is registered. A meter may automatically recognize the existence of the more reliable communication path, switch collectors, and notify the previous collector that the change has taken place. The process of switching the registration of a meter from a first collector to a second collector begins when a registered meter 114 receives a node scan request from a collector 116 other than the one with which the meter is presently registered. Typically, a registered meter 114 does not respond to node scan requests. However, if the request is likely to result in a more reliable transmission path, even a registered meter may respond. Accordingly, the meter determines if the new collector offers a potentially more reliable transmission path. For example, the meter 114 may determine if the path to the potential new collector 116 comprises fewer hops than the path to the collector with which the meter is registered. If not, the path may not be more reliable and the meter 114 will not respond to the node scan. The meter 114 might also determine if the RSSI of the node scan packet exceeds an RSSI threshold identified in the node scan information. If so, the new collector may offer a more reliable transmission path for meter data. If not, the transmission path may not be acceptable and the meter may not respond. Additionally, if the reliability of communication between the potential new collector and the repeater that would service the meter meets a threshold established when the repeater was registered with its existing collector, the communication path to the new collector may be more reliable. If the reliability does not exceed this threshold, however, the meter 114 does not respond to the node scan.

If it is determined that the path to the new collector may be better than the path to its existing collector, the meter 114 responds to the node scan. Included in the response is information regarding any nodes for which the particular meter may operate as a repeater. For example, the response might identify the number of nodes for which the meter serves as a repeater.

The collector 116 then determines if it has the capacity to service the meter and any meters for which it operates as a repeater. If not, the collector 116 does not respond to the meter that is attempting to change collectors. If, however, the collector 116 determines that it has capacity to service the meter 114, the collector 116 stores registration information about the meter 114. The collector 116 then transmits a registration command to meter 114. The meter 114 updates its registration data to identify that it is now registered with the new collector. The collector 116 then communicates instructions to the meter 114 to initiate a node scan request. Nodes that are unregistered, or that had previously used meter 114 as a repeater respond to the request to identify themselves to collector 116. The collector registers these nodes as is described above in connection with registering new meters/nodes.

Under some circumstances it may be necessary to change a collector. For example, a collector may be malfunctioning and need to be taken off-line. Accordingly, a new communication path must be provided for collecting meter data from the meters serviced by the particular collector. The process of replacing a collector is performed by broadcasting a message to unregister, usually from a replacement collector, to all of the meters that are registered with the collector that is being removed from service. In one embodiment, registered meters may be programmed to only respond to commands from the collector with which they are registered. Accordingly, the command to unregister may comprise the unique identifier of the collector that is being replaced. In response to the command to unregister, the meters begin to operate as unregistered meters and respond to node scan requests. To allow the unregistered command to propagate through the subnet, when a node receives the command it will not unregister immediately, but rather remain registered for a defined period, which may be referred to as the “Time to Live.” During this time to live period, the nodes continue to respond to application layer and immediate retries allowing the unregistration command to propagate to all nodes in the subnet. Ultimately, the meters register with the replacement collector using the procedure described above.

One of collector's 116 main responsibilities within subnet 120 is to retrieve metering data from meters 114. In one embodiment, collector 116 has as a goal to obtain at least one successful read of the metering data per day from each node in its subnet. Collector 116 attempts to retrieve the data from all nodes in its subnet 120 at a configurable periodicity. For example, collector 116 may be configured to attempt to retrieve metering data from meters 114 in its subnet 120 once every 4 hours. In greater detail, in one embodiment, the data collection process begins with the collector 116 identifying one of the meters 114 in its subnet 120. For example, collector 116 may review a list of registered nodes and identify one for reading. The collector 116 then communicates a command to the particular meter 114 that it forward its metering data to the collector 116. If the meter reading is successful and the data is received at collector 116, the collector 116 determines if there are other meters that have not been read during the present reading session. If so, processing continues. However, if all of the meters 114 in subnet 120 have been read, the collector waits a defined length of time, such as, for example, 4 hours, before attempting another read.

If during a read of a particular meter, the meter data is not received at collector 116, the collector 116 begins a retry procedure wherein it attempts to retry the data read from the particular meter. Collector 116 continues to attempt to read the data from the node until either the data is read or the next subnet reading takes place. In an embodiment, collector 116 attempts to read the data every 60 minutes. Thus, wherein a subnet reading is taken every 4 hours, collector 116 may issue three retries between subnet readings.

Meters 114 are often two-way meters—i.e. they are operable to both receive and transmit data. However, one-way meters that are operable only to transmit and not receive data may also be deployed. FIG. 4 is a block diagram illustrating a subnet 401 that includes a number of one-way meters 451-456. As shown, meters 114 a-k are two-way devices. In this example, the two-way meters 114 a-k operate in the exemplary manner described above, such that each meter has a communication path to the collector 116 that is either a direct path (e.g., meters 114 a and 114 b have a direct path to the collector 116) or an indirect path through one or more intermediate meters that serve as repeaters. For example, meter 114 h has a path to the collector through, in sequence, intermediate meters 114 d and 114 b. In this example embodiment, when a one-way meter (e.g., meter 451) broadcasts its usage data, the data may be received at one or more two-way meters that are in proximity to the one-way meter (e.g., two-way meters 114 f and 114 g). In one embodiment, the data from the one-way meter is stored in each two-way meter that receives it, and the data is designated in those two-way meters as having been received from the one-way meter. At some point, the data from the one-way meter is communicated, by each two-way meter that received it, to the collector 116. For example, when the collector reads the two-way meter data, it recognizes the existence of meter data from the one-way meter and reads it as well. After the data from the one-way meter has been read, it is removed from memory.

While the collection of data from one-way meters by the collector has been described above in the context of a network of two-way meters 114 that operate in the manner described in connection with the embodiments described above, it is understood that the present invention is not limited to the particular form of network established and utilized by the meters 114 to transmit data to the collector. Rather, the present invention may be used in the context of any network topology in which a plurality of two-way communication nodes are capable of transmitting data and of having that data propagated through the network of nodes to the collector. As a result, time-of-use and interval data collection functionality can be restored more quickly. Recovering the clock reference data in this way may also facilitate determining the duration of the power outage.

According to the disclosure herein, clock reference data may be recovered or updated in networks that include line-powered devices and other devices susceptible to power outages. For example, for a mobile information collection network, one or more devices with extended clock holdover may be strategically deployed throughout the mobile information collection network to provide reference clock data. As another example, battery-powered devices may be woken up in order to provide clock reference data to other devices. Alternatively or additionally, the battery-powered devices may be configured to periodically broadcast their clock reference data to other devices.

In greater detail, one of the techniques disclosed herein may involve strategically deploying extended clock holdover devices throughout a mobile information collection network in order to provide clock reference data. The extended clock holdover device may be, for example, a gatekeeper device, a collector device and/or a battery backed repeater device. Such devices may often include a battery which may keep the device powered for an extended duration after a power outage has occurred.

As should be appreciated, devices such as gatekeepers are common in fixed networks such as, for example, Advanced Metering Infrastructure (AMI) systems. In such fixed networks, the gatekeeper devices provide a data extraction point for downstream devices such as gas, water and electricity meters. By contrast, mobile information collection networks such as, for example, Automatic Meter Reading (AMR) systems typically do not include devices such as gatekeepers. Instead, in mobile information collection networks, data is extracted by a mobile device that travels to the physical proximity of the devices from which it extracts information.

FIG. 5A depicts an exemplary prior art mobile information collection network. As shown, the network 500 includes nodes 502, which may include devices such as, for example, electricity meters. Information is extracted from the nodes 502 using a mobile device 506 that travels within a physical proximity of each node 502 in order to collect information from each node 502.

FIG. 5B depicts an exemplary mobile information collection network with an extended clock holdover device 510. As shown in FIG. 5B, an establishment of communications between extended clock holdover device 510 and nodes 502 may cause fixed communication paths 504 to be established between the extended clock holdover device 510 and at least some of the nodes 502. In the event of a power outage or another event requiring a clock update, the fixed paths 504 may allow clock reference data to be provided by extended clock holdover device 510 to the nodes 502. As should be appreciated, however, fixed paths 504 may often not serve as a mechanism for which information such as metering data is collected from nodes 502. Rather, information such as metering data may continue to be collected from nodes 502 by the mobile device 506 just as in the prior art system of FIG. 5A.

In a mobile deployment without network or local gatekeepers or other network devices with clock holdover, or after a prolonged power outage event or in other scenarios, the internal clock of a battery-powered endpoint device, such as a gas or water communication module, can be used to recover a reference clock. After restoration of power, meter points may not have a valid reference clock and may not be able to recover the clock from a local, e.g., RF-accessible, fixed network point that is always on, e.g., a line-powered device. Should this occur, the battery-powered endpoint devices may often have a local clock that can be provided to the always-on network points as a reference clock. While this clock may not be the preferred reference, it can be used in the absence of other clock sources until a higher precision clock source becomes available. For a mobile network, a higher precision clock may be made available by the actual mobile data collection device. However, the mobile data collection device may not pass the meters that lost the clock reference for days or weeks. Having the ability to capture a local clock source shortly after power is restored, as opposed to having to wait for a collection device to pass, allows the reestablishment of the reference clock for time-of-use and interval data collection purposes. It may also enable the calculation of the duration of the power outage.

When the battery-powered devices are operating in a fixed network, they typically communicate to electricity meters only infrequently (for example, every four hours) and send a message with metering data. After sending this message, the battery-powered devices may listen for additional requests from devices that received the message. In a mobile environment, the battery-powered device may be configured to periodically wake up (for example, every three seconds) and listen for a wake-up message. If a wake-up message is received, the battery-powered device may then listen for a communication request, respond to the request or requests if any have been received, and then return to a low-power sleep mode. Some battery-powered devices may operate in a “hybrid” mode in which the battery-powered devices are configured to support both fixed and mobile network communications. In such a hybrid mode, the battery-powered device may listen for the wake-up message, but at a slower rate (for example, every ten seconds), and also periodically send the fixed network data message whether or not a wake-up message has been received.

In one example embodiment, the battery-powered device operates in a mode in which it is configured to work with a mobile network. In the mobile mode, the battery-powered device may listen for a wake-up tone periodically (for example, every three seconds) and operate in a low-power sleep mode for the remainder of the time. In conventional mobile information collection networks, the battery-powered devices are typically woken up by the mobile data collection device in order to provide information such as metering data to the mobile data collection device. However, according to the present disclosure, the battery-powered devices may also be woken up by other devices such as electricity meters and other line-powered devices in order to provide clock reference data to such other devices.

Each electricity meter may be associated with one or more battery-powered devices. Typically, a battery-powered device, such as a gas or water metering device, is associated with the electricity meter that serves the same residence. After a power failure occurs that causes the electricity meter to lose its clock, the electricity meter may send a wake-up message to the gas or water metering device followed by a time request message. The response from the battery-powered device may provide the electricity meter with the clock reference data, e.g., date and time.

Not all electricity meters need to be associated with a battery-powered device. In some networks, only a subset of electricity meters is associated with battery-powered devices. Additionally, an electricity meter need not necessarily be associated with a battery powered device in order to request the clock reference data from that battery powered device. The electricity meters that receive time data from a battery-powered device may then be responsible for broadcasting or otherwise propagating the time data to other electricity meters in the network. The electricity meter configuration may determine whether time is requested from battery-powered devices and/or if time is then broadcast to other electricity meters.

FIG. 6 is a process flow diagram illustrating an example method 600 for obtaining clock reference data from a battery-powered device. At a step 602, the line-powered device detects a power restoration subsequent to a power failure. As should be appreciated, events other than a power failure may also cause a need to obtain or update clock reference data. At a step 604, the line-powered device transmits a wake-up signal to the battery-powered device. The line-powered device also sends a request for a clock reference to the battery-powered device at a step 606. At a step 608, the line-powered device receives the clock reference data from the battery-powered device. At a step 610, the line-powered device may update its internal clock reference data in accordance with the clock reference data received from the battery-powered device. At a step 612, the line-powered device may broadcast the received clock reference data to other devices.

In some embodiments, the battery-powered device may be configured for a fixed network mode of operation in which the battery-powered device periodically broadcasts information such as metering data to “upstream” devices, which may include, for example, electricity meters. The electricity meters may then forward the information further upstream to, for example, gatekeepers and/or collectors. The techniques described herein may allow clock reference data to be transmitted by the battery-powered device as part of a fixed network information message to upstream devices. In this mode of operation, the battery-powered device may operate in a low-power sleep mode when not transmitting and may not be configured to be woken via a wake-up message. The delay period between transmissions of the fixed network messages including the clock reference data from the battery-powered devices may be variable.

In yet other embodiments, the battery-powered device may be configured for a “hybrid” mode of operation, in which the battery-powered device both periodically listens for a wake-up message, as in the mobile network mode of operation, and periodically broadcasts a fixed network message regardless of whether a wake-up message has been received, as in the fixed network mode of operation. In this scenario, the battery-powered device may listen for a wake-up message less frequently (for example, every ten seconds) as compared with a battery-powered device 506 that is configured for strictly a mobile network mode of operation (for example, every three seconds). The battery-powered device may broadcast the fixed network message (for example, every four hours). Similarly to the mobile-only configuration, the electricity meter may transmit a wake-up message after power is restored and the clock was not maintained. Due to the less frequent wake-up interval from the battery-powered device 506, the duration of the wake-up message from the electricity meter may be longer than is involved for a battery-powered device that is configured for a mobile network mode of operation.

In addition to these configuration parameters, devices such as electricity meters can have other configuration parameters set to control the behavior relative to receiving clock reference data. For example, a “clock allowed” configuration parameter may define the devices from which clock reference data may be accepted. A set of “clock preference” configuration parameters may define the preferred clock sources and may define an order of priority of the preferred clock sources.

Devices such as electricity meters may also maintain not only the clock, but also the identity of the device from which clock reference data was most recently received. If valid clock reference data is received from an allowed source having a higher priority than the device from which clock reference data was most recently received, the current meter clock may be replaced with the clock from the source having the higher priority.

FIG. 7 is a process flow diagram illustrating an exemplary method for updating clock reference data. At a step 702, clock reference data is received from a first source. For example, an electricity meter might receive clock reference data from a battery-powered device such as a gas or water meter. At a step 704, internal clock reference data is updated. For example, the electricity meter might update its internal clock with the reference data received from the battery-powered device. At a step 706, the rank of the first source is stored. For example, the electricity meter may maintain a record that its “current” clock reference data was obtained from the battery-powered device, which may be a lower ranked device with lower precision data. The rankings may be based on order of priority of clock reference data which may be stored by the electricity meter. At a step 708, clock reference data is received from a second source. For example, when the mobile device eventually moves within a physical proximity of the electricity meter, the mobile device may provide its clock reference data to the electricity meter. At a step 710, it is determined whether the second source is ranked higher than the first source. If the second source is ranked higher than the first source, then the clock reference data from the second source may be used to update the internal clock reference data at a step 714. At a step 716, the rank of the second source is stored. For example, the electricity meter may determine that the mobile device is a higher ranked source than the battery-powered device and may responsively update its internal clock reference data with the data from the mobile device. The electricity meter may also maintain a record that its “current” clock reference data has now been obtained from the mobile device. If, on the other hand, at step 710, it were determined that the second source was not ranked higher than the first source, then the clock reference data from the second source may be disregarded at a step 712.

The types of devices that may provide clock reference data may include, but are not limited to, fixed network infrastructure devices, such as gatekeepers and/or collectors, repeaters, other electricity meters, or other line-powered devices; mobile data collection devices; battery-powered devices, such as gas and water communication devices; and home area network (HAN) devices. HAN devices may communicate via one or more types of radios. For example, HAN devices may use the 900 MHz radio that is used for fixed network and mobile communications between devices and the fixed network or mobile network data collector. HAN devices may also communicate to electricity meters via different radio such as a 2.4 GHz radio. Multiple devices in the HAN may have valid clocks, and HAN devices may be further prioritized to define the preferred HAN device or devices.

In one example embodiment, the order of priority of sources for clock reference data may be as follows. Fixed network gatekeeper and/or collector devices may have the highest priority. Fixed network repeater devices or other line-powered devices may have the next highest priority. Mobile network collector devices may have the next highest priority after line-powered devices. Battery-powered communication modules may have the next highest priority after mobile network collector devices. HAN devices may have the lowest priority, with network-controlled HAN devices potentially having higher priority than non-network-controlled HAN devices.

All or portions of the subject matter disclosed herein may be embodied in hardware, software, or a combination of both. When embodied in software, the methods and apparatus of the subject matter disclosed herein, or certain aspects or portions thereof, may be embodied in the form of program code (e.g., computer executable instructions). This program code may be stored on a computer-readable medium, such as a magnetic, electrical, or optical storage medium, including without limitation, a floppy diskette, CD-ROM, CD-RW, DVD-ROM, DVD-RAM, magnetic tape, flash memory, hard disk drive, or any other machine-readable storage medium, wherein, when the program code is loaded into and executed by a machine, such as a computer or server, the machine becomes an apparatus for practicing the invention. A device on which the program code executes will generally include a processor, a storage medium readable by the processor (including volatile and non-volatile memory and/or storage elements), at least one input device, and at least one output device. The program code may be implemented in a high level procedural or object oriented programming language. Alternatively, the program code can be implemented in an assembly or machine language. In any case, the language may be a compiled or interpreted language. When implemented on a general-purpose processor, the program code may combine with the processor to provide a unique apparatus that operates analogously to specific logic circuits.

While systems and methods have been described and illustrated with reference to specific embodiments, those skilled in the art will recognize that modification and variations may be made without departing from the principles described above and set forth in the following claims. Accordingly, reference should be made to the following claims as describing the scope of the present invention. 

What is claimed is:
 1. A system for efficient update of clock reference data after a power outage in a mobile information collection network, the system comprising: one or more mobile mode communication nodes configured to communicate information to a mobile device when the mobile device moves within a physical proximity of the mobile mode communication nodes; and an extended clock holdover node configured to maintain the clock reference data after the power outage for a longer duration than the mobile mode communication nodes; wherein, after power is restored at the mobile mode communication nodes, the extended clock holdover node is configured to provide the clock reference data to the mobile mode communication nodes.
 2. The system of claim 1, wherein the extended clock holdover node comprises a gatekeeper device, a collector device or a battery backed repeater device, and wherein at least some of the mobile mode communication nodes comprise electricity meters.
 3. The system of claim 1, wherein the mobile mode communication nodes each store a ranked list of available sources from which to obtain clock reference data.
 4. The system of claim 3, wherein the ranked list comprises the extended clock holdover node, the mobile device, battery-powered devices and home area network (HAN) devices.
 5. The system of claim 3, wherein the mobile mode communication nodes are configured to override clock reference data received from a lower ranked source when different clock reference data is subsequently received from a higher ranked source.
 6. In a system comprising a plurality of mobile mode communication devices configured to communicate information to a mobile device when the mobile device moves within a physical proximity of the mobile mode communication devices, at least one of the mobile mode communication devices being a battery-powered device, a method for obtaining clock reference data from the battery-powered device, the method comprising: sending a wake-up signal to the battery-powered device; sending a clock reference request signal to the battery-powered device; and receiving the clock reference data from the battery-powered device.
 7. The method of claim 6, wherein the wake-up signal is transmitted by a line-powered device to the battery-powered device after power is restored from an outage that caused the line-powered device to lose a valid date and time source, and wherein the line-powered device requests and receives date and time from the battery-powered device.
 8. The method of claim 6, wherein the battery-powered device operates in a repeating cycle in which it sleeps, then wakes-up to listen for a wake-up signal, and then either receives a wake up signal to communicate information or returns to sleep without receiving a wake-up signal.
 9. The method of claim 6, wherein the battery-powered device operates in a hybrid mode in which it is configured to transmit the clock reference data after being woken up and also periodically transmits the clock reference data as part of a fixed network message.
 10. The method of claim 6, further comprising broadcasting to other devices the clock reference data received from the battery-powered device.
 11. The method of claim 6, further comprising storing a ranked list of available sources from which to obtain clock reference data.
 12. The method of claim 11, wherein the ranked list comprises an extended clock holdover node, the mobile device, battery-powered devices and home area network (HAN) devices.
 13. The method of claim 11, further comprising overriding clock reference data received from a lower ranked source when different clock reference data is subsequently received from a higher ranked source.
 14. The method of claim 6, wherein the battery-powered device is a water or gas meter and the clock reference data is received by an electricity meter.
 15. In a fixed wireless network comprising a plurality of communication nodes in wireless communication with a control node, each communication node having a wireless communication path to the control node that is either a direct path or an indirect path through one or more other communication nodes that serve as repeaters, a system for obtaining clock reference data by a line-powered communication node, the system comprising: the line-powered communication node; and a battery-powered communication node that periodically transmits clock reference data as part of a fixed network message, wherein the line-powered communication node is configured to receive the clock reference data transmitted by the battery-powered communication node.
 16. The system of claim 15, wherein the battery-powered communication node operates in a hybrid mode in which it is configured to transmit the clock reference data after being woken up and also periodically transmits the clock reference data as part of the fixed network message.
 17. The system of claim 15, wherein the line powered communication node is an electricity meter and wherein the battery-powered communication node is a gas or water meter.
 18. The system of claim 15, wherein the line-powered communication node stores a ranked list of available sources from which to obtain clock reference data.
 19. The system of claim 18, wherein the ranked list comprises an extended clock holdover node, a mobile device, battery-powered devices and home area network (HAN) devices.
 20. The system of claim 18, wherein the line-powered communication node is configured to override clock reference data received from a lower ranked source when different clock reference data is subsequently received from a higher ranked source. 